A Novel PAR-1-Type Thrombin Receptor Signaling Pathway: Cyclic AMP-Independent Activation of PKA in SNB-19 Glioblastoma Cells

Abstract Cellular effects of thrombin are mediated by members of a new subfamily of G protein-coupled receptors designated proteinase-activated receptors (PARs) with the prototype PAR-1. Investigation of PAR-1-induced signaling has been shown to be very important in clarifying thrombin‘s role in cell metabolism, differentiation, and growth. We evaluated connection of PAR-1 with the cAMP/PKA pathway in SNB-19 glioblastoma cells. Alpha-thrombin and the synthetic PAR-1 agonist SFLLRN stimulated PKA as shown by increased PKA activity and translocation of the catalytic PKA α subunits (PKA cat α) into the nucleus. However, no effect on cAMP could be observed. PKA cat α was found to be associated with nuclear factor-kappa B (NF-κB) p65 and its inhibitor protein IκB in SNB-19 cells. After PAR-1 stimulation, this association was markedly diminished. We conclude that PAR-1 mediates PKA activation without altering cAMP levels but includes NF-κB-associated PKA cat α in SNB-19 glioblastoma cells. This is the first evidence for a cAMP-independent PKA signaling by a G protein-coupled receptor.